The XLSB file format is a spreadsheet file format used by Microsoft Excel. It's a binary file format, meaning it stores data in a more compact and efficient way compared to the older .XLS format or the XML-based .XLSX format. This binary structure allows for faster opening and saving of large Excel files, especially those containing complex formulas, charts, and formatting. XLSB files can store multiple worksheets, charts, macros, and other Excel-related data. They are often preferred when performance is a critical factor, such as when dealing with very large datasets or complex calculations. While XLSX is more widely compatible with other spreadsheet applications, XLSB offers a performance advantage within the Microsoft Excel ecosystem. It's important to note that while XLSB files can contain macros, users should still exercise caution when opening files from untrusted sources, as malicious macros can pose a security risk. The format is supported by Excel versions 2007 and later.